The present invention relates to a wafer cassette transfer machine and method for transferring semiconductor wafers between wafer cassettes having different registration mechanisms.
In present semiconductor wafer processing systems, all of the wafer cassettes ordinarily utilized in a particular processing system have the same registration features on their bottom surfaces for properly aligning the wafer cassettes on a support surface of a “one-way” the wafer transfer machine. The one-way wafer transfer machine includes a mechanism having a “plunger” or wafer-pushing member that engages the edges of, for example, 25 wafers in a loaded wafer cassette and pushes all of the wafers therein simultaneously into an adjacent, precisely aligned empty standard wafer cassette. Wafer transfer machines must be designed using structures and materials which are compatible with a wafer fabrication environment and avoid any risk of semiconductor wafer breakage, and also avoid any kind of friction that generates minute “particulates” which can become airborne and then become deposited on the surfaces of the semiconductor wafers. This is because such particulates can cause processing defects that result in malfunction of the integrated circuits formed thereon.
There is a known anodized aluminum wafer cassette for high-temperature wafer processing (hereinafter referred to as the “ASM high-temperature cassette”) manufactured by Advanced Semiconductor Manufacturing, Inc. and specially designed for high-temperature wafer processing in certain reactors manufactured by the same company. In some cases, it may be desirable to use the high temperature anodized aluminum wafer cassettes for carrying semiconductor wafers during high-temperature processing operations, and to use “semi-standard” PFA Teflon cassettes (hereinafter referred to simply as “Teflon cassettes”) for carrying the same wafers during other low temperature processing operations. (“Semi-standard” cassettes also can be made of other plastic material, such as polyethylene or polypropylene, that is suitable for the wafer fabrication environment.) However, the PFA Teflon cassettes and the ASM high-temperature cassettes have different bottom registration features. Consequently, the ASM high-temperature cassettes cannot be used in any single available wafer transfer machine to transfer semiconductor wafers from either (1) the “semi-standard” PFA Teflon cassettes into the ASM high-temperature cassettes or (2) the ASM high-temperature cassettes into the PFA Teflon cassettes. Instead, two separate wafer transfer machines are required. There has been no practical, fast, economical way of accomplishing the two foregoing kinds of wafer transfer operations when it is desirable to use both kinds of cassettes. Also, automated robotic systems that transfer only one wafer at a time was known in the art.
Thus, there is an unmet need to avoid the expense, inconvenience, and space required to use two separate wafer transfer machines to accomplish transfer of wafers in either direction between two different kinds of cassettes, especially cassettes having incompatible registration features. Consequently, there is an unmet need for a single inexpensive wafer transfer machine and method that can rapidly accomplish simultaneous transfer of an entire cassette load of wafers in a single pass between two different kinds of cassettes having incompatible registration features.